1. Technical Field
The present invention relates to an ink-jet ink set.
2. Related Art
In ink-jet recording processes, achromatic images printed with a black ink only have a granular texture in some cases when the achromatic images are light in color. In order to prevent the occurrence of the granular texture, a black ink, a yellow ink, a magenta ink, and a cyan ink are used in combination to form an achromatic region as known. However, in the case of using dyes as colorants for these inks, there is a problem in that an achromatic image becomes colored due to fading.
In order to cope with the problem, JP-A-2008-297356 discloses an ink set for ink-jet recording. The ink set has an object to prevent an achromatic region from being colored even in the case where the achromatic region is exposed to air for a long period and therefore is faded by ozone in air. The ink set includes a dye yellow ink, a dye magenta ink, a dye cyan ink, and a dye black ink. In the case where a patch is formed using each ink and is subjected to a predetermined ozone resistance test and the rate of reduction in optical density (hereinafter referred to as “OD value”) of the patch is investigated by the ozone resistance test, the order of magnitude of the rate of reduction in OD value of a yellow component, magenta component, and cyan component in the patch formed using the dye black ink is opposite to the order of magnitude of the rate of reduction in OD value of a yellow component in the patch formed using the dye yellow ink, a magenta component in the patch formed using the dye magenta ink, and a cyan component in the patch formed using the dye cyan ink.
However, in the case of recording a low-duty region using a conventional ink set, sufficient ozone resistance cannot be achieved in some cases when the amount of dye applied to a recording medium is small. In other words, the ozone resistance of an image recorded in a low-duty region may possibly be lower than the ozone resistance of an image recorded in a high-duty region (for example, a duty of 100%). Therefore, an ink-jet ink set capable of providing an achromatic image with excellent ozone resistance not only in a high-duty region but also in a low-duty region is desired.
In an ink set including a black ink containing carbon black, in the case of recording an achromatic image in a low-duty region using the black ink only, the achromatic image may possibly have a granular texture. Therefore, an ink-jet ink set capable of providing an achromatic image with a reduced granular texture (hereinafter referred to as excellent granularity) even in a low-duty region is desired.